Oleander Leaf Scorch & Oleander Alternatives

The oleanders on our hill are turning brown. I have noticed many in our neighborhood in the same condition. Is there something we can do to save them?
Flo Tyler, Woodland Hills
Your oleanders (Nerium oleander) have fallen victim to oleander leaf scorch, or OLS for short. There is no cure for this bacterial disease, whose symptoms appear, at first glance, to be a sign of insufficient moisture.
A plant lacking water will have distressed shoots throughout its foliar canopy. In the case of OLS, shoots on only one part of the plant initially turn brown.
It has been said that watering and fertilizing diseased oleanders can extend their life, but this has not been clearly demonstrated. It may be wiser, in fact, to destroy affected plants because the disease is easily spread. The vector for dissemination of OLS is a 1/2-inch-long, glassy-winged sharpshooter insect — a kind of leafhopper. The sharpshooter is identifiable by its wings, which rest tent-like upon its back, and its movements, which consist of brusque, quicker-than-lightning hops.
The bacterium involved lives in the water-conducting xylem tissue of the plant. Thus, in sucking sap from the plant, the leafhopper ingests bacteria that multiply in its saliva and then are passed along to neighboring oleanders when the insect visits them to feed. Bacteria that take up residence in a leafhopper’s saliva continue to do so for the rest of the insect’s life.
It is not easy to find a comparable replacement for oleander, which flowers heavily in red, pink, white or salmon for many months on little, if any, water. A program for selection and breeding of OLS-resistant varieties makes sense, as some oleanders, such as ‘Petite Pink’ and ‘Petite Salmon’ seem less disease-prone than others.
In terms of size, Italian buckthorn (Rhamnus alaternus) has been suggested as an oleander alternative, as it grows into a plant of similar dimensions. Italian buckthorn is a lush, drought tolerant evergreen with luminous foliage that is more cold tolerant than oleander. Yellow oleander (Thevetia peruviana), with butter yellow blooms, has taken the place of the diseased red, pink and white flowering oleanders in some areas. However, yellow oleander is more cold-sensitive and, in general, less robust than common oleander.
Why are my Eureka lemons so huge with thick rinds? Often the insides are dried out by the end of May. The tree is planted on the south side of our lot beside the lawn, so it gets plenty of sun, water and fertilizer. We planted it 12 years ago, and for the first couple of years the lemons were normal sized and very juicy, with very large crops. The tree gets pruned to 8-10 feet every year. I’d like to get a moderate crop over several months, but now the lemons aren’t worth saving except for deodorizing the garbage disposal. I need your input ASAP.
Mrs. Robert Schick, Northridge
Citrus trees for orchard and backyard use consist of two different but related plants grafted together. In the nursery, the bud of a lemon (Citrus limon) variety such as `Eureka,’ for example, is grafted onto the shoot of a species often grown from seed, such as Citrus macrophylla. As the bud of `Eureka’ grows into a shoot, all shoots of Citrus macrophylla are removed. Thus, the only shoots, leaves and, eventually, fruit that appear on the grafted tree will belong to the `Eureka’ variety.
In horticultural language, `Eureka’ is called the scion and Citrus macrophylla is called the rootstock. Rootstock species are selected for the vigor they impart to the scion.
So how was your `Eureka’ tree transformed into something else? As you probably know, lemon trees have a tendency to produce suckers. Suckers are shoots that sprout from the base of the trunk, below the point where the original scion bud was grafted onto the rootstock. Suckers, should they be allowed to develop, will produce fruit of the rootstock species. Rootstock fruit is invariably inferior to the fruit produced by the scion. What has probably happened to your tree is that a sucker, or suckers, from the Citrus macrophylla rootstock have outgrown and smothered the `Eureka’ scion. The fruit you see is from Citrus macrophylla, a species whose fruit has the thick rinds and limited pulp that you describe.
At this point, there is really nothing you can do to salvage your tree. I would recommend removing it and planting another unless you want to keep it for ornamental purposes.
Tip of the week: Organic, biodegradable deer and rabbit repellents are now available. They can be sprayed on all plants, including edibles. Reapplication is required every 45 days. You can learn more about keeping wildlife out of the garden through use of these repellents at www.messinawildlife.com.

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Welcome to The Smarter Gardener. I'm Joshua Siskin and I've been writing about plants and trees for the Los Angeles Daily News for over 20 years. If you have any questions or comments, please send them along. I have published more than 1,000 articles on plants and I am currently in the process of loading them onto this site. My goal is to make it possible for you to learn about any of the plants in your garden by doing a search of this site.